The present invention relates generally to sandwich constructions for use in structural and non-structural members, and more particularly to corrugated sandwich constructions for use in applications requiring high-strength, light-weight components.
Sandwich constructions are finding broad application as structural and non-structural members in boats, aircraft, furniture, refrigerators, and other items requiring high strength, light-weight materials. In airplane design in particular the need for weight efficiency and aerodynamically smooth surfaces under high stress levels has stimulated use of such sandwich constructions. A typical sandwich construction includes face sheets bonded to either side of a low-density core. The honeycomb core sandwich constructions are considered to be among the most weight-efficient, but they have a tendency to retain moisture which may become entrapped due to ineffective edge seals, damage to the face sheets, or unbonding of the face sheets from the core. Retained moisture may degrade the construction's structural integrity and lead to extensive corrosion and premature failure. Another type of sandwich construction incorporates corrugated sheet as its core. This construction suffers from a similar moisture retention problem, in that moisture can only escape in a direction parallel to the peaks and troughs of the corrugations.
In U.S. Pat. No. 5,348,601 issued to Hemen Ray on Sep. 20, 1994, there is disclosed a low-density sandwich construction with an open core that makes it self-venting. It comprises corrugated strips having planar peaks and troughs, arranged adjacent to and parallel with each other, with the peaks and troughs of adjacent strips being 180 degrees out of phase with each other. This creates a plurality of passage-ways through which moisture can escape. Such a construction has good bending strength in the direction perpendicular to the corrugated strips, but less bending strength in the transverse direction. The method of making such a construction requires the use of variously-shaped mandrels, and further requires the use of a two-step curing process because midway through the process the solid mandrels must be replaced with a granular material.
In U.S. Pat. No. 5,162,143 issued to Porter on Nov. 10, 1992, there is disclosed a sandwich construction having a core which is made up of a plurality of criss-crossed corrugated strips. The corrugated strips cross at their peaks and troughs. To manufacture the construction, forming protrusions are positioned on a base, and the corrugated strips are placed over the protrusions to form the peaks of the corrugations. One protrusion is required for each peak crossing point. The criss-crossed strips are then cured to form the core of the sandwich construction. The forming protrusions are then removed, and face sheets are adhesively bonded to the core. This construction thus does not overcome the face sheet unbonding problem from which sandwich constructions suffer.
Generally, designers of sandwich constructions seek to optimize lightness of weight, strength (including bending strength in more than one direction), ease of manufacture, and minimization of future maintenance problems caused by moisture retention and unbonding of the face sheets of the construction.